The present invention relates generally to a display system, and more particularly to a display system of compact size and low power consumption.
Among compact display systems, there is a direct-viewing type liquid crystal display system. These compact display systems, for the most part, are used with cellular phones and portable terminals. For high-definition display purposes, on the one hand, display systems comprising an increased number of pixels are needed. For moving image display purposes, on the other hand, display systems having fast display speeds are required. Such requirements are satisfied by use of active matrix liquid crystals. However, the active matrix liquid crystals are expensive, and consume large power with the need of large capacity batteries for presenting displays over an extended period of time.
Some arrangements using a small display device and designed to present images appearing on that display device on an enlarged scale through an optical system are disclosed in JP-A 48-102527, and JP-A 5-303054 filed by the applicant. In these arrangements, the images appearing on the display systems are magnified through a concave mirror and displayed as virtual images. In the latter arrangement in particular, a non-rotationally symmetric reflecting surface is used to obtain projected images with reduced aberrations.
There is also available a projection optical system proposed by the applicant in JP-A's 5-303055 and 2000-221440. In this projection optical system, an image displayed on a display device is once projected in midair to form a projected image. Then, the projected image is magnified by a concave mirror for display purposes.
Display systems, for instance, are disclosed in JP-A's 7-270781 and 9-139901.
Further, the applicant has already field Japanese Patent Application No. 2001-66669 to come up with a compact, low power consumption display system. In this display system, a relay optical system and an eyepiece optical system are used to set up an optical system. In this optical system, the relay optical system comprises a decentering prism optical system. Then, an image or its intermediate image (hereinafter called simply the image) appearing on the display device is projected near the eyepiece optical system. The eyepiece optical system also serves to converge a light beam from the relay optical system toward the eyeball of an observer. At this time, the eyepiece optical system projects the exit pupil of the relay optical system onto a given position. Here the given position is understood to mean the position of the eyeball of the observer upon observation.
For the optical system comprising a relay optical system and an eyepiece optical system, the eyepiece optical system must be decentered so as to reduce its overall size. Then, the relay optical system is located such that light rays emerging therefrom are obliquely incident on the eyepiece optical system. The relay optical system is also positioned such that its exit pupil is located at either one of two focuses F, F′ of such a spheroid as shown in FIG. 1. In this state, the eyeball of the observer is brought in alignment with the position of another focus (F or F′). Even in the decentered arrangement, there is thus no pupil aberration at all.
However, the eyepiece optical system must be constructed of a large concave mirror that has a large thickness and so offers troublesome problems in connection with portability and handleability.
To avoid these problems, it is known to construct the eyepiece optical system using a transmission or reflection type Fresnel lens.